1. Field of the Invention
The present invention relates to a condenser inserted between a compressor and an evaporator in a vapor compression type refrigerator, which is used for an automobile air conditioner. The condenser receives the refrigerant from the compressor, condenses and liquefies the refrigerant by causing it to radiate heat, and sends the liquefied refrigerant to an evaporator by way of a liquid tank.
2. Description of the Related Art
A vapor compression type refrigerator is incorporated into an automobile air conditioner for cooling and dehumidifying the inside of an automobile. A circuit diagram showing the concept of the vapor compression type refrigerator, disclosed in Japanese Patent Publication No. Hei. 4-95522, is shown in FIG. 14. A compressor 1 discharges a gaseous refrigerant that is high in temperature and pressure to a condenser 2. When passing through the condenser 2, a heat exchanging is performed between the refrigerant and air. The gaseous refrigerant drops in temperature and is condensed into a liquid refrigerant. The liquid refrigerant is temporarily impounded in a liquid tank 3. Then, it is sent through an expansion valve 4 to an evaporator 5 where it is evaporated. Temperature of the evaporator 5 drops because the evaporator loses the latent heat of vaporization. Therefore, when air for air conditioning is circulated through the evaporator 5, the air is cooled and dehumidified. The refrigerant is evaporated into a gaseous refrigerant in the evaporator 5, and is sucked by and into the compressor 1, and compressed again therein. In this way, the refrigerating cycle is repeated.
FIG. 15 shows a condenser 2 to which the present invention is applied. As shown, the condenser 2 includes a couple of upper and lower header pipes 6a and 6b arranged horizontally and in parallel. Refrigerant vertically flows between the upper and lower header pipes 6a and 6b. The condenser 2 is of the so-called vertical flow type. Attempts have been made to use fins for the cores of both the condenser 2 and a radiator 26 located adjacent to the condenser, and thereby realize a compact assembly of the condenser 2 and the radiator 26. One or more partitioning walls are provided within the header pipes 6a and 6b of the condenser 2, whereby the inner parts of the header pipes 6a and 6b are air- and liquid-tightly partitioned into a plural number of chambers. The inner part of the upper header pipe 6a is partitioned, by an upper partitioning wall 13, into a first upper chamber 15 and a second upper chamber 16. The inner part of the lower header pipe 6b is partitioned, by a lower partitioning wall 14, into a first lower chamber 17 and a second lower chamber 18. In the core 9 of the condenser 2, a plural number of heat transfer tubes 7 are vertically arranged between the upper and lower header pipes 6a and 6b. Fins 8 are located between and supported by the heat transfer tubes 7 located adjacent to each other. Those heat transfer tubes 7 are classified into three types of heat transfer tubes, first heat transfer tubes 19, second heat transfer tubes 20, and third heat transfer tubes 21. The first heat transfer tubes 19 are opened at the upper ends into the first upper chamber 15, and at the lower ends into the first lower chamber 17. The second heat transfer tubes 20 are opened at the upper ends into the second upper chamber 16, and at the lower ends into the first lower chamber 17. The third heat transfer tubes 21 are opened at the upper ends into the second upper chamber 16, and at the lower ends into the second lower chamber 18. The heat transfer tubes 7 are grouped into the first to third heat transfer tubes 19, 20 and 21 with respect to the upper and lower partitioning walls 13 and 14. The first heat transfer tubes 19 are located most upstream in the core, and feed the refrigerant downward. The second heat transfer tubes 20 are located at the central portion of the core, and feed the refrigerant upward. The third heat transfer tubes 21 are located most downstream in the core, and feed the refrigerant downward. Side plates 10a and 10b are located on both sides of the core 9 including the heat transfer tubes 7 and the fins 8.
The first, second and third heat transfer tubes 19, 20 and 21 are different in number. A total passage area S19 of the first heat transfer tubes 19 is larger than a total passage area S20 of the second heat transfer tubes 20, and the total passage area S20 is larger than a total passage area S21 of the third heat transfer tubes 21. That is, S19&gt;S20&gt;S21. (However, in the case of a condenser 2 shown in FIG. 16, S19=S20=S21, and the first, second and third heat transfer tubes 19, 20 and 21 are equal in number.) That is, the total passage area of one group (upward group or downward group) of the heat transfer tubes is generally decreased as the refrigerant flows downward because the refrigerant is more condensed as flowing downward so that the volume of the refrigerant is more decreased.
An incoming block 11 is brazed to the upper side of right end (in FIG. 15) of the upper header pipe 6a. The incoming block 11 includes incoming ports 12 continuous to the inside of the first upper chamber 15. Refrigerant that comes in through the incoming ports 12 flows vertically between the upper and lower header pipes 6a and 6b in the direction of arrows in FIG. 15.
An outgoing pipe 22 through which the refrigerant goes out is firmly attached to the lower side of the left end (in FIG. 15) of the lower header pipe 6b, viz., the lower surface of the leftmost chamber (second lower chamber 18) located most downstream in the condenser. The upper end of the outgoing pipe 22 is opened into the second lower chamber 18 at a position close to the lower partitioning wall 14. The refrigerant flows into the condenser 2, flows through the condenser 2 in the direction of the arrows (FIG. 15), and reaches the second lower chamber 18 of the lower header pipe 6b. Then, the refrigerant goes out of the outgoing pipe 22, flows through the liquid tank 3 and the expansion valve 4, and goes to the evaporator 5 (FIG. 14). In FIG. 16, the outgoing pipe 22 is omitted.
In the inner part of the thus constructed condenser 2, refrigerant that comes in from the compressor 1 (FIG. 14) flows while being condensed into a liquid refrigerant. Specifically, the refrigerant comes in the condenser 2 through the incoming ports 12, and as it is passed through the condenser 2, heat exchange is carried out between the refrigerant and air that flows through the core 9 in the direction from one side to the other side of the core 9, thereby dropping the temperature of the refrigerant. Thus, the gaseous refrigerant comes in the condenser 2 and is separated into a liquid refrigerant and a gaseous refrigerant. Therefore, the liquid refrigerant and the gaseous refrigerant coexist in the third heat transfer tubes 21.
FIG. 17 shows another example of the conventional condenser 2. In this condenser, the outgoing pipe 22 is attached to the upper side of the left end of the upper header pipe 6a, viz., the upper surface of the leftmost chamber located most downstream in the condenser. That is, two upper partitioning walls 13 are provided in the upper header pipe 6a.
In the condenser 2 shown in FIG. 17, the outgoing pipe 22 is inserted into the upper header pipe 6a through a connection hole 30, which is formed in the upper side of the upper header pipe 6a, and is opened into the upper header pipe 6a. The outer circumferential surface of the outgoing pipe 22 is air- and liquid-tightly coupled with the inner circumferential edge of the connection hole 30 by brazing as shown in FIG. 18. The upper ends of the heat transfer tubes 7 are inserted into the upper header pipe 6a through the connection hole 31 formed in the lower side of the upper header pipe 6a. The upper opening 33 of each heat transfer tube 7 is positioned at the middle of the upper header pipe 6b when viewed in cross section. When an amount of the liquid refrigerant staying in the upper header pipe 6a is small (at high load), a liquid level L1 of the liquid refrigerant is below the opening 32 of the outgoing pipe 22 (FIG. 18). When the liquid refrigerant is large (at low load), a liquid level L2 of the refrigerant reaches the opening 32 of the outgoing pipe 22.
Here, the term "high load" means that a difference between a set temperature in the air conditioner and an actual temperature in the car is large, and the refrigerant frequently circulates in the air conditioner. The term "low load" means that a difference between the set temperature and the actual temperature is small, and the refrigerant infrequently circulates in the air conditioner.
When the amount of liquid refrigerant staying in the upper header pipe 6a is small, the liquid level L1 of the refrigerant is below the opening 32 of the outgoing pipe 22. Therefore, no refrigerant flows into the outgoing pipe 22. The result is that the amount of the liquid refrigerant fed from the condenser 2 to the expansion valve 4 is reduced, temperature drop of the evaporator 5 (FIG. 14) is small, and hence the air conditioner exhibits insufficiently its cooling capability.
When the liquid refrigerant staying in the upper header pipe 6a is large in amount, the liquid level L2 of the refrigerant is above the opening 32 of the outgoing pipe 22. The air conditioner does not suffer from the above problem, but suffers from the following problem. Since the liquid level L2 of the refrigerant increases above the upper openings 33 of each heat transfer tube 7, the refrigerant that has ascended through the heat transfer tubes 7 flows into the upper header pipe 6a while pushing aside the liquid refrigerant that stays in the upper header pipe 6a. Since a viscosity of the liquid refrigerant is larger than that of the gaseous refrigerant, the liquid refrigerant exhibits a large resistance to the thrust by the gaseous refrigerant. Therefore, when the refrigerant ascends through the heat transfer tubes 7 and flows into the upper header pipe 6a, it undergoes an increased impedance. In other words, a resistance of the condenser 2 is increased. The increase of the resistance of the condenser 2 leads to degradation of the performances of the vapor compression type refrigerator having the condenser 2 incorporated therein.
Further, a lubricant is mixed into the refrigerant to lubricate the compressor. In the conventional condensers constructed as aforementioned, the lubricant tends to gather in the condenser 2, thereby lessening the amount of lubricant that circulates through the refrigerating cycle in the vapor compression type refrigerator. The lubricant mixed into the refrigerant circulates, together with the refrigerant, through the refrigerating cycle in the refrigerator while lubricating the compressor. The opened, upper ends of the heat transfer tubes 7 of the core 9 of the condenser 2 are protruded into the inside of the upper header pipe 6a and their tips are positioned at the mid position therein when viewed in cross section (FIGS. 19 and 20).
The lubricant 34 that is mixed into the refrigerant flows into the upper header pipe 6a and tends to be gathered on the bottom of the upper header pipe 6a. The lubricant mixed into the refrigerant will gradually be separated from the refrigerant with time. After being separated from the refrigerant in the upper header pipe 6a, the lubricant 34 (in FIGS. 19 and 20) is gathered in the space between the bottom surface of the upper header pipe 6a and the upper end openings of the heat transfer tubes 7, viz., on the bottom of the upper header pipe 6a. The lubricant 34 that is gathered on the bottom of the upper header pipe 6a only flows a little in the direction of flow of refrigerant. Therefore, the amount of the lubricant 34 that circulates through the refrigerating cycle in the vapor compression type refrigerator is reduced by the amount of the lubricant gathered on the bottom of the upper header pipe 6a. In an extreme case, the amount of the lubricant 34 that circulates through the refrigerating cycle in the vapor compression type refrigerator is reduced below a necessary amount thereby impairing the durability of the compressor.
The durability impairing problem may be solved by increasing an amount of lubricant put into the refrigerating cycle by an amount equal to the amount of the lubricant that will be gathered on the bottom of the upper header pipe 6a. However, increasing the lubricant amount creates another problem; films of the lubricant tend to be formed on the inner surfaces of the heat transfer tubes which form a heat exchanger (including the evaporator and the condenser). Presence of the lubricant films on the heat transfer tubes hinders the heat exchanging between the refrigerant flowing through the heat transfer tubes and the heat transfer tubes. The result is that the performance of the heat exchanger is degraded. The increase of the lubricant amount further increases the cost to manufacture a vapor compression type refrigerator having the condenser 2 incorporated therein.
To reduce the amount of the lubricant 34 gathered on the bottom of the upper header pipe 6a, a structure as shown in FIGS. 21 and 22 has been proposed. In the structure, the bottom of the upper header pipe 6a is flat. A protrusion of the upper ends of the heat transfer tubes 7 from the flat bottom 35 is reduced. However, the structure suffers from the following problems. In this structure, the bottom 35 is large in area and a depth of the gathered lubricant 34 is not large, but the amount of the lubricant 34 gathered on the bottom of the upper header pipe 6a is increased. When the flat bottom 35 receives a high pressure refrigerant that is fed to the upper header pipe 6a, it is easily deformed. Therefore, where this structure is used, it is difficult to make a good comprise between high durability and reduction of the condenser weight by thinning the upper header pipe 6a.
There is another problem with the condenser shown in FIG. 15. The lower end openings of the third heat transfer tubes 21, which are located closer to the center (closer to the right-hand side in FIG. 15) of the core 9, are confronted with the upper end opening of the outgoing pipe 22. Therefore, an increased amount of the liquid refrigerant tends to flow through those third heat transfer tubes 21 closer to the core center. The reason for this is as follows. The liquid refrigerant that flows toward the left end (in FIG. 15) of the upper header pipe 6a in the second upper chamber 16 will flow downward by its weight. As a result, an increased amount of the liquid refrigerant flows into the third heat transfer tubes 21 that are located closer to the center of the core 9. The liquid refrigerant that flows into the third heat transfer tubes 21 directly reaches the upper end opening of the outgoing pipe 22, and is discharged out of the condenser 2. Meanwhile, the gaseous refrigerant is in a high velocity of flow, and less affected by its weight. Therefore, the gaseous refrigerant reaches the end of the second upper chamber 16 that is located downstream in the core, and flows downward through the third heat transfer tubes 21 (laid out in the cross-hatched portion in FIG. 15) located close to the left end of the core 9, and reaches the left end portion (in FIG. 15) of the second lower chamber 18. The gaseous refrigerant then flows to the center in the second lower chamber 18, and goes out of the condenser 2, through the outgoing pipe 22.
If the liquid refrigerant and the gaseous refrigerant that pass through the third heat transfer tubes 21 are mixed in the second lower chamber 18 and go out of the outgoing pipe 22, no problem arises in particular. The gaseous refrigerant that reaches the left end of the second lower chamber 18, swiftly moves to a portion near to the upper end of the outgoing pipe 22. Sometimes, the gaseous refrigerant is obstructed by the liquid refrigerant temporarily staying at a portion close to the right end of the second lower chamber 18, and fails to reach the upper end opening of the outgoing pipe 22. The gaseous refrigerant that fails to reach the upper end opening of the outgoing pipe 22 stays in the second lower chamber 18, thereby collecting an excess amount of gaseous refrigerant. Then, the gaseous refrigerant rushes into the outgoing pipe 22 because of its increased pressure. Where this phenomenon is repeated, only the liquid refrigerant and the mixture of the liquid refrigerant and the gaseous refrigerant are alternatively discharged through the outgoing pipe 22. The refrigerant discharging operation from the outgoing pipe 22 is thus instable. The result impair the temperature control function of the automobile air conditioner.
Further, there is still another problem in the condenser in FIGS. 15 and 16.
The lubricant tends to gather at a portion B (shaded in FIGS. 15 and 16) within the lower header pipe 6b. Portion B is close to the lower partitioning wall 14 which partitions the inner space of the lower header pipe 6b into the first lower chamber 17 and the second lower chamber 18. The reason for this is that after flowing through the first heat transfer tubes 19 into the first lower chamber 17, the refrigerant flows to the second heat transfer tubes 20 while pushing the lubricant against the lower partitioning wall 14. The refrigerant then flows upward through the second heat transfer tubes 20. If the flow velocity of the refrigerant flowing through the first lower chamber 17 to the lower partitioning wall 14 is sufficiently large, it pushes the lubricant into the second heat transfer tubes 20. In the structure of either condenser of FIGS. 15 and 16, the flow velocity is not sufficiently large. Therefore, when the refrigerant flows upward through the second heat transfer tubes 20, the lubricant mixed into the refrigerant remains in the vicinity of the lower partitioning wall 14. The amount of lubricant fed to the compressor is reduced by the amount of lubricant staying in the condenser 2, and deficient. This problem frequently arises particularly when the amount of the refrigerant discharged out of the compressor is small and a reduced amount of the refrigerant flows through the condenser 2, for example, when the engine is idling, and when the compressor of the variable capacity type is reduced in its capacity.